1. Field of the Invention
The present invention relates to an ink jet printer head for printing by ejecting ink on a print medium and more particularly to an ink jet printer head including a cavity plate formed with parallelogram-shaped ink pressure chambers.
2. Description of the Related Art
U.S. Pat. No. 4,680,595 discloses an ink jet printer head with a laminated configuration forming a plurality of pressure chambers and an actuator unit spanning across the pressure chambers. The pressure chambers are arranged next to each other and each has an election nozzle, The actuator unit includes a plurality of piezoelectric elements disposed on a single diaphragm plate. The piezoelectric elements are arranged in a one-to-one correspondence with the pressure chambers.
Japanese Patent-Application Publication No. HEI-3-114654 discloses an ink jet recording head with a plurality of pressure chambers and a laminated piezoelectric actuator spanning across the pressure chambers. The pressure chambers are arranged mutually next to each other and each has an ejection nozzle. The actuator includes a plurality of electrodes arranged in a one-to-one correspondence with the pressure chambers. Ink is ejected from the nozzles by applying a voltage to one of the piezoelectric elements so that the portion of the actuator that corresponds to the pressure chamber deforms to protrude or retract in order to apply pressure to the ink in the corresponding pressure chamber. The ink in the pressure chamber is ejected out through the nozzle by the pressure.
U.S. Pat. No. 5,402,159 discloses an ejector array made up of an ink channel body and a laminated piezoelectric actuator. The ink channel body is formed with ink channels in a one-to-one correspondence with ink ejecting orifices. The actuator is fixedly secured to the ink channel body. The piezoelectric actuator is made up of piezoelectric ceramic layers, internal negative electrode layers shared by all the ink channels, and internal positive electrode segments aligned with corresponding ink channels. The piezoelectric actuator has piezoelectric active regions sandwiched between the internal negative layer and the internal positive electrode layer segments.
Japanese Examined-Patent-Application-Publication No. HEI2-4429 and U.S. Pat. No. 5,087,930 disclose ink jet printer heads with a cavity plate formed with lemon-shaped pressure chambers. The ink jet printer head of Japanese Examined-Patent-Application-Publication No. HEI-2-4429 includes a rectangular cavity plate formed with the pressure chambers aligned in two coaxial arc-shaped columns. Ink ejecting nozzles are positioned at the substantial axial center on the arc shapes. One acute-angled portion of each pressure chamber faces the ejection nozzles and is formed with an ink channel connected to one of the ejection nozzles. U.S. Pat. No. 5,087,930 discloses an ink jet printer head with two pressure chamber columns provided in a staggered arrangement for a single row of ink ejection nozzles. Pressure chamber in both columns have one acute-angled portion aligned with the row of ink ejection nozzles. Connecting passageways connect the acute-angled portions with the ink ejection nozzles.
U.S. Pat. No. 4,680,595 and in Japanese Patent-Application Publication No. HEI-3-114654 describe rectangular shaped pressure chambers aligned in parallel with each other with a single actuator spanning across all of the pressure chambers. As shown in FIG. 1, when an actuator 50 is positioned across a plurality of pressure chambers 51a, 51b, 51c, when the actuator 50 deforms at a portion 50a corresponding to one pressure chamber 51a, the actuator portions 50b, 50c that correspond to adjacent chambers 51b, 51c will deform in the opposite direction with partition walls 52a, 52b serving as fulcrums. This results in cross-talk, wherein undesirable fluctuations in pressure are inevitably generated in the ink in the adjacent pressure chambers 51a, 51c and when ink is again ejected from the same pressure chamber 51a, the fluctuations in pressure overlap so that a predetermined ink ejection cannot be obtained.
Although the ink jet printer heads disclosed in Japanese Examined-Patent-Application-Publication No. HEI-2-4429 and U.S. Pat. No. 5,087,930 achieve a compact size by using lemon-shaped ink pressure chambers, problems arise when the number of nozzles for ejecting ink is increased to produce a color ink jet head.
For example, it is impossible to concentrate the nozzle columns for ejecting ink. That is, the ink jet printer head disclosed in Japanese Examined-Patent-Application-Publication No. HEI-2-4429 has ejection nozzles that open to the same edge surface of the cavity plate, so the only way to increase the number of nozzles is to provide a plurality of cavity plates stacked on top of each other. The ink jet printer head disclosed in U.S. Pat. No. 5,087,930 requires a pair of pressure chamber columns for each row of nozzles, that is, for each different ink color. The different nozzle rows must be separated by two column""s distance.
Also, the ink jet printer head must be attached with great precision. That is, ink droplets from corresponding nozzles of adjacent nozzle columns should impinge on that same position of the recording medium. However, when nozzle columns are greatly separated from each other, ink droplets from corresponding nozzles can impinge on the recording medium at different positions if the head is even slightly slanted with respect to a relative movement between the ink jet head and the recording medium.
When pressure chambers are aligned in the manner described in U.S. Pat. No. 5,087,930, the only way to increase the density of pressure chamber columns in the ink jet printer head is to shorten the distance from the ink supply opening to the nozzle connecting passageway of the pressure chambers. By doing this, pressure waves can propagate from one end of the pressure chamber to other in a much shorter time, and so the ink ejection cycle can be shortened. However, a certain amount of time is required from when voltage is first applied to drive a piezoelectric element to when the voltage reaches a predetermined voltage required to deform the piezoelectric element. This is termed the rising-edge time of the voltage. If rising-edge time of the voltage is longer than the time required for the pressure wave to propagate once across the pressure chamber, then the piezoelectric actuator cannot be driven efficiently, which defeats the benefit of making the pressure chamber shorter. Further, if the distance from the ink supply port and the ink ejection nozzles in the pressure chambers is shortened excessively in order to increase the density of pressure chamber columns, the actuators, such as piezoelectric elements, cannot deform into the pressure chambers by an amount sufficient to properly eject droplets.
The arrangements disclosed in Japanese Examined-Patent-Application-Publication No. HEI-2-4429 and U.S. Pat. No. 5,087,930 include pressure chambers that are adjacent to each other in the direction in which they are shifted to produce the staggered arrangement. These adjacent pressure chambers have broad edges in confrontation with each other. Cross talk is a problem with these arrangements because of these confronting edges.
It is an objective of the present invention to overcome the above-described problems and to provide an ink jet print head with a plurality of ink pressure chambers that correspond to a plurality of nozzles aligned in columns without increasing dimensions of the cavity plate.
It is another objective of the present invention to provide an ink jet printer head with reduced cross talk and stable predetermined ink ejection.
In order to achieve the above-described objectives, an ink jet printer head according to one aspect of the present invention includes a cavity plate and an actuator with the following configuration.
The cavity plate is formed with at least a first, second, and third column of pressure chambers. Each pressure chamber has a substantial parallelogram shape with two acute-angle portions. One acute-angle portion is formed with an ink supply opening. The other acute-angle portion is formed with an ink ejection nozzle opening. The pressure chambers in the first and second columns are arranged so that the ejection-nozzle-side acute-angle portions of chambers in one column are interposed between ejection-nozzle-side acute-angle portions of pressure chambers of the other column. The pressure chambers of the third column are arranged so that ejection-nozzle-side acute-angle portions are interposed between the ink-supply-side acute-angle portion of pressure chambers in either the first or second columns.
The actuator is disposed in confrontation with the pressure chambers of the cavity plate and applies ejection pressure to the ink in the ink pressure chambers.
Because the pressure chambers have substantially the shape of a parallelogram with acute angles, a large number of pressure chambers can be provided in the cavity plate without increasing the size of the cavity plate. When the pressure chambers of the first, second, and third columns are arranged with acute-angle portions interposed in this manner, the ink jet nozzles of the first or second columns can be positioned in close proximity to each other. The ink jet nozzles of the third column can be positioned much closer to the ink jet nozzles of the first and second columns than if the ink-supply-side acute-angle portions were interposed between the ink-supply-side acute-angle portions of pressure columns of the first or second column. Also, because the ink supply ports and the ink nozzle ports are provided in the opposing acute-angle portions formed in the parallelogram-shaped ink pressure chambers, even if the pressure chamber columns are provided at a high density, a suitable distance can be opened between the ink supply ports and the ink ejection nozzle ports. As a result, the drive waveform of the drive voltage can have a slower rising edge time and the actuator can deform by a sufficient amount.
An ink jet printer head according to a second aspect of the present invention includes a cavity plate and an actuator with the following configuration.
The cavity plate is formed with a plurality of pressure chambers, nozzles, and ink supply sources. Each pressure chamber is connected to a corresponding nozzle through one end of the pressure chamber and to a corresponding ink supply source through the other end of the pressure chamber. Each pressure chamber has a pair of confronting parallel side walls that define therebetween a principal portion. The pressure chambers are arranged so that parallel lines defined by the side walls of each pressure chamber are parallel with parallel lines defined by side walls of adjacent pressure chambers, and also so that the principal portions are shifted out of alignment with each other in a direction extending parallel with the side walls.
The actuator unit is disposed across the plurality of pressure chambers and includes a plurality of pressure generating portions at positions that correspond to the pressure chambers.
Because the principal portions are shifted out of alignment in this manner, cross talk can be prevented.